Means for perforating and fracturing earth formations



B. E. KENLEY 3,118,501

MEANS FOR PERFORATING AND FRACTURING EARTH FORMATIONS Jan. 21, 1964 Filed May 2, 1960 BRE/VTS E. KENLEY @M WZSHZ@ MSX Eldar/m43 United States Patent O f 3,118,501 MEANS FR PERFORATEG AND FRACTURING EARTH FURMATINS Brents E. Kenley, Z317 31st St., Lubbock, Tex. Filed May 2, 196i), Ser. No. 26,101 4 Claims. (Cl. MAS-55.4)

The invention disclosed herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention relates to new and useful improvements in methods and means for perforating and fracturing earth formations.

There are many Wells, especially petroleum Wells, in which a producing `formation is penetrated by the well bore, but in which the permeability or porosity of the formation is not sufficiently high as to permit adequate or the desired iiow of liquids, such as petroleum fluids, into the well bore for recovery. It has been the practice to acidize these formation faces with inhibited acid solutions or mixtures, to detonate explosive charges adjacent the formation faces, or otherwise to process the well bore in an effort to increase the flowing capacity thereof. These various practices all have certain objections, however, and have not always been completely successful or satisfactory.

It has also been the practice, in completing a producing well, to set Well casing in the well bore in a bed or sheathing of cement or other suitable material and then to form perforations through the casing and the cement into the producing formation for recovery of the desirable fluids. In some instances, projectiles in the nature of bullets are employed and are shot from a multiplicity of guns lowered into the Well bore, and in other instances, jet perforating charges, utilizing the shaped charge effect, have been employed for the same purpose. Often, following perforation of the well by projectiles or jet perforation charges, an acidizing treatment is carried out, or more commonly in recent years, a pressure fracturing operation in which liquids are introduced under high pressure into `the well bore for creating cracks and lissures, or opening up existing cracks and fissures in the producing formation, the fluids normally being mixed with quantities of a propping material such as sand, gravel, andthe like, which will enter into the open fissures and prevent them from again closing after the pressure is reduced. This, of course, requires two operations upon the well bore and the running of two sets of tools into the well bore, a time-consuming and expensive process.

This application is a continuation in part of my copending application Serial Number 707,895 filed January 9, 1958 and now abandoned.

The present invention contemplates the lowering of perforating equipment'into the well bore in such manner that a suitable high pressure may be applied Within the portion of the well casing in the Zone of the producing formation and while such pressure is maintained, the explosive perforating charges are detonated to create a high pressure peak supplementing the previously applied pressure and at the same time perfor-ating passages through the casing into the earth formation to which said said pressure peak is instantaneously applied. In this manner, the perforation and fracturing of the well bore may be carried out in a single operation with a single running `of equipment into the well bore whereby more effective results are obtained, and also whereby a more economical preparation of the well for final completion is achieved. The invention also contemplates the obtaining of higher pressures for fracturing of the formation than heretofore has been safely employed, as well as pressure loading of the well casing, when so desired,

3,118,5l Patented Jan. 21, 1964 ICC presently obtainable by standard fracturing procedures.r

A further object of the invention is to provide an improved method and means for perforating and fracturing well formations in which the well tubing is protected from excessive pressure surges, and in which the well casing may be protected when so desired.

Yet another object of the invention is to provide an improved method and means for perforating and fracturing well formations in which both the fracturing and perforating operations may be carried out by a single running of equipment into the well bore whereby the time and expense of multiple trips into the well are avoided.

Still a further object of the invention is to provide 4improved methods and means for perforating and fracturing Well formations in which more effective and extensive fracturing of the formation is obtained, and which may be utilized in a cased well bore.

An additional object of the invention is to provide improved methods and means of perforating and fracturing well formations in which the minute cracks and fissures normally present in an earth formation are effectively opened up for considerable distances back from the well bore to provide for increased flow of well fluids, and in which the application of a high loading pressure concurrently with the detonation of explosive well perforating equipment permits the utilization of the inherent crumbling of rock particles for propping open the cracks and yfractures so obtained, or in which additional fluids containing propping materials such as sand and gravel may be introduced into the well bore for flow into the cracks and crev-ices Without reduction of the pressure being applied to the Well formation.

A construction designed to carry out the invention will be hereinafter described, together with other features of the invention.

The invention will be more readily understood from a reading of the following specification and by reference to the accompanying drawing wherein an example of the invention is shown, and wherein:

FIG. l is a longitudinal, sectional view, partly in eleva- -tion and partly' in section, illustrating equipment constructed in accordance with this invention and adapted to carry out the methods hereof, the view being taken of the equipment prior to the perforating and fracturing step;

FIG. 2 is a view similar to FIG. 1 illustrating more or less schematically the equipment and the well bore following the perforating and fracturing step; and

FIG. 3 is a sectional View of the check valve and associated passages taken along the line 3 3 of FIG. 1.

In the drawings, the numeral 10 designates an earth formation which normally includes a plurality of various strata spaced at vertical elevations and which may consist of shale, limestone, and various other similar materials. A well bore 11 penetrates the earth formation into a producing formation or strata 12 which may be any of several varying types and which is shown on a largely schematic basis and somewhat exaggerated as to depth with respect to the remaining formations. Normally, a well casing or pipe 13 is anchored or set in the well bore by means of an underlying layer 14 of concrete or other suitable material, the casing extending into the producing formation 12, as illustrated. The casing is provided at its upper end with a casing head having a pressure connection 16 leading thereto through a valve 17, there also being provided a tubing 18 having an exposed valve 19 and extending downwardly through the casing head through suitable sealing structures common in this art to a packer 20 positioned at or near the upper face of the producing formation 12. The packer may be of any suitable or desirable type, as well known to those skilled in this art, and is set within the casing 13 to seal off the annulus between the tubing 18 and the casing.

Below the packer 20, a check valve 21 is fastened to the end of tubing 18 by a nipple 36. Check valve 21 comprises a ball mounted in a bore 31 of a casing 32. Ball 30 is yieldably held against seat 33 by a spring 34. Formed in casing 32 above seat 33 is a small bleed orifice 35. A nipple 37 connects the lower end of valve 21 to a fitting 38 provided with a vertical bore 39 and a horizontal bore which permits uid passing through check valve 21 to enter the casing 11 below packer 20 in the zone of the producing formation or strata 12.

Mounted below the fitting 38 is a suitable gun tiring mechanism 22 having a perforating gun structure 23 fastened therebelow.

This invention is not concerned with particular types of perforating guns or gun tiring mechanisms, these being quite varied and well known in this art, and being adapted to be fired by electrical impulses originating at the ground surface, by electrical impulses originating within the gun firing structure through batteries and a pre-set timing mechanism, through pressure surges applied through the tubing or the casing, or by any of the other various and well known types of gun firing instrumentalities. Further, the perforating gun itself may be of the projectile tiring type, or more desirably, of the jet perforating charge type utilizing a shaped charge of explosive for perforating the well bore and the well casing and its cement bedding layer. The perforating gun illustrated schematically in the drawings is of the recoverable or retrievable type, but obviously, any suitable type of perforating structure may be employed. Of course, the number and spacing of the perforating charges will depend upon the thickness of the formation, its porosity or permeability in some instances, and thus, in general, the number of perforations desired in the well wall. All of this well perforating art is quite standard and well known, is subject to much variation, and need not be discussed further at this point.

In carrying out the processes of this invention, the perforating gun 23 is lowered into the well bore and set in position below the packer 20 as illustrated in FIG. 1, the tubing 18 extending upwardly through the well bore to the ground surface for reception of a pressure fluid. Water, oil or other suitable fluid is applied under pressure to tubing 18 by pump 24 through valve 19. Pressure is also placed above packer 20 in the well casing 13 through valve 17, piping 16 and well cap 15 to assist in holding the packer against upward movement when fracturing and by pressure generated by firing of the perforating gun 23.

The pressure, which may be in the order of 5,000 lbs. per square inch, placed on tubing 18 will be of a magnitude sufficient to fracture the formation or to continue the fracturing process initiated by the peak pressure, which may range from 10,000 lbs. to 50,000 lbs. per square inch, developed by tiring the perforating gun.

Fluid under pressure passes through check valve 21 through the openings 40 in fitting 38 and into the casing 13 below packer 20. While the check valve permits uid to ow down tubing 18 and into the casing, it will not permit uid to flow from the casing into the tube. It can be seen that any pressure in the casing higher than that in the tubing will cause ball 30 of check valve 21 to close against seat 33 thus effectively preventing the higher pressure from entering tubing 18.

Fluid under fracturing pressure pumped into casing 13 completely surrounds firing mechanism 22 and pcrforat ing gun 23 and ils the casing below packer 20.

Where prior art processes are used the pressure level attained in the zone of the formation is limited to the pressure which the tubing can withstand. By the use of valve 21 this limitation is avoided in the process of the present invention.

With pump 24 maintaining fracturing pressure in casing 13 below packer 20 the tiring mechanism 22 dctonatcs the perforating gun 33 in any desired manner. Upon detonation of gun 23, the casing 13, cement 14 and the formation 12 are perforated, and simultaneously the pressure surrounding the gun and the area within the casing below packer 20 rises to a peak. This peak pressure of liquid is generated by the explosive contained in gun 23. At the same time due to the increased pressure, check valve 21 closes and the liquid is forced by the pressure through the perforations in the casing into the producing formation 12. Check valve 21 being closed, the increased pressure cannot enter tubing 18 through the valve. Bleed orifice 35 is of such size that the rate of ow of fluid into tubing 18 will be negligible and will not npprcciably increase pressure within the tube during the period of peak pressure.

The peak pressure will be lowered as the fluid passes through the perforations and into the cracks and crevices of the formation. When the pressure in the casing below packer 20 lowers to that of the fracturing pressure applied in tubing 18 check valve 21 opens, thus to continue the application of at least fracturing pressure on the formation.

If desired, at this time a propping agent may be pumped into the formation through tubing 13 without reduction of pressure. When a predetermined quantity of the propping agent has been mixed with the fracturing fluid, the flow of the propping agent is stopped, and without drop in pressure the ow of fracturing fluid is continued into the tubing 18 until the tubing and casing are flushed of the propping agent. Thus it is seen that the process can be carried out without dropping the pressure below fracturing pressure from perforation of the casing until completion of the ushing operation.

The high peak pressure assures high penetration of the formation and maintenance of at least fracturing pressure on cracks and crevices of the formation results in the establishment of very extensive openings, crevices and the like, thus greatly increasing the porosity or permeability of the producing formation.

The bleed orifice 35 is for bleeding pressure in casing 11 below packer 20 back up the tubing 18 when pump pressure in the tubing is lowered and it is desired to lower the casing pressure. The pressure is bled off through oritice 35 and the gun withdrawn without a long wait until the pressure is reduced by seepage to a safe condition.

The perforating of the formation, along with the simultaneous fracturing thereof, will cause extensive crumbling and cracking of the walls and channels of the various cracks and crevices so that on release of the fracturing pressure, these cracks and crevices will not again close up to their previously very small and tight configurations. If desired, as aforesaid, the firing of the perforating gun may be immediately followed by the pumping into the well bore of suitable propping uids which may consist of water, oil, or other suitable uids having suspended therein quantities of sand, gravel, or other material which will be carried into the body of the producing formation in the cracks and crevices formed therein so as to act as props or blocks to prevent closing of the cracks and crevices after pressure is reduced.

As heretofore mentioned, the casing 13 above packer 20 may also be placed under a predetermined pressure both to protect the casing against possible collapse during the perforating operation is referred\to herein as fracturing pressure, and it is pointed out thatthis pressure may vary quite considerably depending upon the depthof the well bore and the type of producing formation encountered. The pressure may be as low as a thousand or two thousand pounds per square inch, or may be considerably higher, and normally is that pressure required for slight opening of the cracks and crevices in the face of the producing formation, or the pressure required to cause slight upward or downward shifting of the portions of the producing formation above and below the cracks and crevices. Often, this pressure is referred to as that necessary to lift slightly the overburden which represents the downward pressure being applied to the producing formation by the various earth lformations thereabove. Obviously, no exact limitations can be stated for the magnitude of pressure to be applied in any given case, and therefore, as employed herein fracturing pressure is utilized to designate that pressure suflicient to open to a slight degree the cracks and crevices present in the producing formation.

Of course, while this pressure is maintained and the considerable additional explosive impulse of the perforating gun is added thereto, pressures are momentarily achieved far in excess of that required for slight shifting of the portions of the producing formation, and very effective fracturing and penetration of the formation is obtained.

Following the fracturing and perforating operation, along with the introduction of a propping fluid into the fractured formation if such step be thought desirable, the pressure being applied to the producing formation is reduced to such level as may be consistent with proper completion and handling of the well in question, the pressure being applied to the casing above the packer through connection 16 is then bled olf through the valve 17, packer 2li is released and the tubing withdrawn from the well bore along with the gun firing mechanism 22 and the gun 23 which normally are rather costly and are desirably recovered. Thereafter, the well may be completed in the usual fashion.

Whenever a liquid medium carrying a propping agent is employed, it is usually desirable to carry out a flushing and well cleaning operation to remove this material, and

this, of course, may be done before or after the pressure on the formation is partially or fully removed.

The foregoing description of the invention is explanatory thereof and various changes in the size, shape and materials, as well as in the details of the illustrateel construction may be made, within the scope of the appended claims, without departing from the spirit of the invention.

I claim:

1. Apparatus for perforating and fracturing a low permeability earth formation penetrated by a tubular wall casing comprising, a fluid conveyance tube within said casingr and opening into the portion thereof within the low permeability earth formation, a sealing means interposed between said tube and said casing to form a sealed compartment in the portion of the casing in said earth formation, fluidinjection means connected to said tube to inject fluid through said tube and into said compartment to provide a pressure therein in excess of fracturing pressure, valve means in the portion of said tube located within the compartment constructed so as to permit flow only into lsaid compartment whereby pressurized fluid may be constrained within said compartment; a casing and earth formation perforator within said compartment, and said apparatus including pressure bleed-off means connecting the interior of said compartment with the exterior thereof.

2. Apparatus as set forth in claim l wherein, said valve means is a check valve in said tube, said check Valve being so arranged as to permit fluid flow only into said compartment.

3. Apparatus as set forth in claim l wherein, said pressure bleed-off means comprises a bleed orifice formed in said tube at a point in said tube between the valve means and the sealing means.

4. An apparatus as set forth in claim 2 wherein, said pressure bleed-olf means comprises a bleed orifice formed in said tube at a point in said -tube between the check valve and the sealing means.

References @ited in the tile of this patent UNTED STATES EJATENTS 1,248,698 McAvoy Dec. 4, 1917 2,411,667 Mowrey Nov. 26, 1946 2,623,725 Sands Dec. 30, 1952 2,676,662 Ritzmann Apr. 27, 1954 2,753,940 Bonner July 10, 1956 2,766,828 Rachford Oct. 16, 1956 2,777,523 Brown et al Ian. 15, 1957 2,924,237 Ellis Feb. 9, 1960 3,011,551 Young et al Dec. 5, 1961 

1. APPARATUS FOR PERFORATING AND FRACTURING A LOW PERMEABILITY EARTH FORMATION PENETRATED BY A TUBULAR WALL CASING COMPRISING, A FLUID CONVEYANCE TUBE WITHIN SAID CASING AND OPENING INTO THE PORTION THEREOF WITHIN THE LOW PERMEABILITY EARTH FORMATION, A SEALING MEANS INTERPOSED BETWEEN SAID TUBE AND SAID CASING TO FORM A SEALED COMPARTMENT IN THE PORTION OF THE CASING IN SAID EARTH FORMATION, FLUID INJECTION MEANS CONNECTED TO SAID TUBE TO INJECT FLUID THROUGH SAID TUBE AND INTO SAID COMPARTMENT TO PROVIDE A PRESSURE THEREIN IN EXCESS OF FRACTURING PRESSURE, VALVE MEANS IN THE PORTION OF SAID TUBE LOCATED WITHIN THE COMPARTMENT CONSTRUCTED SO AS TO PERMIT FLOW ONLY INTO SAID COMPARTMENT WHEREBY PRESSURIZED FLUID MAY BE CONSTRAINED WITHIN SAID COMPARTMENT; A CASING AND EARTH FORMATION PERFORATOR WITHIN SAID COMPARTMENT, AND SAID APPARATUS INCLUDING PRESSURE BLEED-OFF MEANS CONNECTING THE INTERIOR OF SAID COMPARTMENT WITH THE EXTERIOR THEREOF. 